Motion vector difference coding extension for enhancement layer

ABSTRACT

An apparatus for coding video information according to certain aspects includes a memory unit and a processor in communication with the memory unit. The memory unit stores difference video information associated with a difference video layer of pixel information derived from a difference between an enhancement layer and a corresponding base layer of the video information. The processor determines pixel accuracy of motion predictor information, determines a motion vector based on the pixel accuracy of the motion predictor information, and determines a value of a video unit based at least in part on the motion vector.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/669,336, filed Jul. 9, 2012, and U.S. Provisional Application No.61/706,467, filed Sep. 27, 2012, the entire contents of which areincorporated by reference.

TECHNICAL FIELD

This disclosure relates to video coding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), the High Efficiency Video Coding (HEVC) standard presentlyunder development, and extensions of such standards. The video devicesmay transmit, receive, encode, decode, and/or store digital videoinformation more efficiently by implementing such video codingtechniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame or a portion of a video frame) may bepartitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures. Pictures may be referredto as frames, and reference pictures may be referred to a referenceframes.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which then may be quantized. Thequantized transform coefficients, initially arranged in atwo-dimensional array, may be scanned in order to produce aone-dimensional vector of transform coefficients, and entropy coding maybe applied to achieve even more compression.

SUMMARY

In general, this disclosure describes techniques related to scalablevideo coding (SVC). More specifically, the techniques of this disclosurerelate to inter prediction in difference domain coding. In someexamples, the techniques may consider motion vector predictorinformation, such as the pixel accuracy of the reference motion vectors,in coding the motion vector delta for the current video unit in thedifference domain. For example, a predictor motion vector with similarpixel accuracy may be given more weight in calculating the value of thecurrent video unit. Similarly, a predictor motion vector from the samedomain, e.g., difference domain, may be given more weight. In someembodiments, the order of the syntax for motion vector delta coding maybe changed in order to provide the motion vector predictor informationprior to providing the motion vector delta information. Accordingly, themotion vector predictor information may be used to code the motionvector delta more efficiently. Moreover, the motion vector predictorinformation may be used to provide additional context information forthe motion vector delta in entropy coding.

An apparatus for coding video information according to certain aspectsincludes a memory unit and a processor in communication with the memoryunit. The memory unit stores difference video information associatedwith a difference video layer of pixel information derived from adifference between an enhancement layer and a corresponding base layerof the video information. The processor determines pixel accuracy ofmotion predictor information, determines a motion vector based on thepixel accuracy of the motion predictor information, and determines avalue of a video unit based at least in part on the motion vector.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques in accordance with aspectsdescribed in this disclosure.

FIG. 2 is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3 is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 4 is a flowchart illustrating an example method for motion vectordifference coding for enhancement layer according to aspects of thisdisclosure.

FIG. 4A is a flowchart illustrating another example method for motionvector difference coding for enhancement layer according to aspects ofthis disclosure.

FIG. 5 is a flowchart illustrating an example method for contextmodeling in the enhancement layer coding according to aspects of thisdisclosure.

DETAILED DESCRIPTION

The techniques described in this disclosure generally relate to scalablevideo coding (SVC). For example, the techniques may be related to, andused with or within, a High Efficiency Video Coding (HEVC) scalablevideo coding (SVC) extension. In an SVC extension, there could bemultiple layers of video information. The layer at the very bottom levelmay serve as a base layer (BL), and the layer at the very top may serveas an enhanced layer (EL). The “enhanced layer” is sometimes referred toas an “enhancement layer,” and these terms may be used interchangeably.All layers in the middle may serve as either or both ELs or BLs. Forexample, a layer in the middle may be an EL for the layers below it,such as the base layer or any intervening enhancement layers, and at thesame time serve as a BL for the enhancement layers above it.

For purposes of illustration only, the techniques described in thedisclosure are described with examples including only two layers (e.g.,lower level layer such as the base layer, and a higher level layer suchas the enhanced layer). It should be understood that the examplesdescribed in this disclosure can be extended to examples with multiplebase layers and enhancement layers as well.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its ScalableVideo Coding (SVC) and Multiview Video Coding (MVC) extensions. Inaddition, a new video coding standard, namely High Efficiency VideoCoding (HEVC), is being developed by the Joint Collaboration Team onVideo Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) andISO/IEC Motion Picture Experts Group (MPEG). A recent draft of HEVC isavailable fromhttp://wg11.sc29.org/jct/doc_end_user/current_document.php?id=5885/JCTVC-I1003-v2,as of Jun. 7, 2012. Another recent draft of the HEVC standard, referredto as “HEVC Working Draft 7” is downloadable fromhttp://phenix.it-sudparis.eu/jct/doc_end_user/documents/9_Geneva/wg11/JCTVC-I1003-v3.zip, as of Jun. 7, 2012. The full citation for the HEVC Working Draft 7is document HCTVC-11003, Bross et al., “High Efficiency Video Coding(HEVC) Text Specification Draft 7,” Joint Collaborative Team on VideoCoding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 9^(th)Meeting: Geneva, Switzerland, Apr. 27, 2012 to May 7, 2012. Each ofthese references is incorporated by reference in its entirety.

Scalable video coding (SVC) may be used to provide quality (alsoreferred to as signal-to-noise (SNR)) scaling, spatial scaling and/ortemporal scaling. An enhanced layer may have different spatialresolution than base layer. For example, the spatial aspect ratiobetween EL and BL can be 1.0, 1.5, 2.0 or other different ratios. Inother words, the spatial aspect of the EL may equal 1.0, 1.5, or 2.0times the spatial aspect of the BL. In some examples, the scaling factorof the EL may be greater than the BL. For example, a size of pictures inthe EL may be greater than a size of pictures in the BL. In this way, itmay be possible, although not a limitation, that the spatial resolutionof the EL is larger than the spatial resolution of the BL.

In coding an enhancement layer, inter prediction may be performed usingeither pixel domain or difference domain. Inter prediction is predictionbased on temporal correlation between video blocks in two frames orslices in sequence of time. For example, the value of a current videoblock being coded may be predicted using a motion vector that indicatesa displacement from the reference video block in a previously codedframe or slice. In SVC, video information can be coded using a baselayer and one or more enhancement layers, and inter prediction can beperformed in the difference domain, e.g., by taking the differencebetween the enhancement layer and the reconstructed base layer. Thedifference domain may refer to a set of difference pixels formed bysubtracting the reconstructed base layer pixels from the original pixelsin the enhancement layer, or vice versa. Inter prediction in thedifference domain can take advantage of the temporal correlation betweenframes as well as the correlation between a base layer and anenhancement layer.

In general, motion vector characteristics are different for differencedomain prediction and non-difference domain (e.g., pixel domain)prediction. For example, the motion vectors may differ in the differenceand non-difference domain in terms of sub-pixel accuracy. The differencedomain generally may have a higher probability of half pixel motionvectors, and the non-difference domain generally has a higherprobability of quarter pixel motion vectors. Therefore, it may not beefficient to use a predictor motion vector from the non-differencedomain in order to code the motion vector delta for a pixel in thedifference domain, and vice versa. Accordingly, it would be advantageousto utilize the information regarding the motion vector characteristicsin coding the motion vector delta for the current pixel.

The techniques described in this disclosure may address issues relatingto inter prediction in the difference domain. The techniques mayconsider the predictor motion vector characteristics in coding themotion vector delta in the difference domain. Such characteristics mayinclude, for example, whether the predictor motion vectors are from thedifference domain or from the non-difference domain, or whether thepixel accuracy of the predictor motion vectors is half pixel, quarterpixel, etc. The information provided in the motion vector predictorinformation, such as the pixel accuracy of the reference motion vectors,may be used to code the motion vector delta for the current video unitmore efficiently. For example, if a predictor motion vector is a quarterpixel, less weight may be given to this predictor motion vector since amotion vector in the difference domain is likely to be a half pixel. Onthe other hand, if a predictor motion vector is a half pixel, moreweight may be given to the prediction motion vector since a motionvector in the difference domain is likely to be a half pixel. Similarly,if a predictor motion vector is from the non-difference domain, it maybe given less weight in predicting the value of the current pixel in thedifference domain. On the other hand, if the predictor motion vector isfrom the difference domain, it may be given more weight. In someembodiments, the order of the syntax for motion vector delta coding maybe changed in order to provide the motion vector predictor informationprior to providing the motion vector delta information.

The techniques described in this disclosure may also use motion vectorpredictor information to determine additional context information usedin entropy coding, e.g., context-adaptive binary arithmetic coding(CABAC). Context information may indicate the probability associatedwith a value being entropy coded. For example, the context informationmay indicate the probability of the entropy coded value being 1, or theprobability of the entropy coded value being 0, etc. The additionalcontext information may be used for coding the motion vector delta ofthe current video unit in the difference domain.

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to any specific structureor function presented throughout this disclosure. Rather, these aspectsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. Based on the teachings herein one skilled in the art shouldappreciate that the scope of the disclosure is intended to cover anyaspect of the novel systems, apparatuses, and methods disclosed herein,whether implemented independently of, or combined with, any other aspectof the invention. For example, an apparatus may be implemented or amethod may be practiced using any number of the aspects set forthherein. In addition, the scope of the invention is intended to coversuch an apparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to or otherthan the various aspects of the invention set forth herein. It should beunderstood that any aspect disclosed herein may be embodied by one ormore elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques in accordance with aspectsdescribed in this disclosure. As shown in FIG. 1, system 10 includes asource device 12 that provides encoded video data to be decoded at alater time by a destination device 14. In particular, source device 12provides the video data to destination device 14 via a computer-readablemedium 16. Source device 12 and destination device 14 may comprise anyof a wide range of devices, including desktop computers, notebook (e.g.,laptop) computers, tablet computers, set-top boxes, telephone handsetssuch as so-called “smart” phones, so-called “smart” pads, televisions,cameras, display devices, digital media players, video gaming consoles,video streaming device, or the like. In some cases, source device 12 anddestination device 14 may be equipped for wireless communication.

Destination device 14 may receive the encoded video data to be decodedvia computer-readable medium 16. Computer-readable medium 16 maycomprise any type of medium or device capable of moving the encodedvideo data from source device 12 to destination device 14. In oneexample, computer-readable medium 16 may comprise a communication mediumto enable source device 12 to transmit encoded video data directly todestination device 14 in real-time. The encoded video data may bemodulated according to a communication standard, such as a wirelesscommunication protocol, and transmitted to destination device 14. Thecommunication medium may comprise any wireless or wired communicationmedium, such as a radio frequency (RF) spectrum or one or more physicaltransmission lines. The communication medium may form part of apacket-based network, such as a local area network, a wide-area network,or a global network such as the Internet. The communication medium mayinclude routers, switches, base stations, or any other equipment thatmay be useful to facilitate communication from source device 12 todestination device 14.

In some examples, encoded data may be output from output interface 22 toa storage device. Similarly, encoded data may be accessed from thestorage device by input interface. The storage device may include any ofa variety of distributed or locally accessed data storage media such asa hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device maycorrespond to a file server or another intermediate storage device thatmay store the encoded video generated by source device 12. Destinationdevice 14 may access stored video data from the storage device viastreaming or download. The file server may be any type of server capableof storing encoded video data and transmitting that encoded video datato the destination device 14. Example file servers include a web server(e.g., for a website), an FTP server, network attached storage (NAS)devices, or a local disk drive. Destination device 14 may access theencoded video data through any standard data connection, including anInternet connection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thestorage device may be a streaming transmission, a download transmission,or a combination thereof.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, Internet streamingvideo transmissions, such as dynamic adaptive streaming over HTTP(DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, system 10 may be configured to supportone-way or two-way video transmission to support applications such asvideo streaming, video playback, video broadcasting, and/or videotelephony.

In the example of FIG. 1, source device 12 includes video source 18,video encoder 20, and output interface 22. Destination device 14includes input interface 28, video decoder 30, and display device 32. Inaccordance with this disclosure, video encoder 20 of source device 12may be configured to apply the techniques for coding a bitstreamincluding video data conforming to multiple standards or standardextensions. In other examples, a source device and a destination devicemay include other components or arrangements. For example, source device12 may receive video data from an external video source 18, such as anexternal camera. Likewise, destination device 14 may interface with anexternal display device, rather than including an integrated displaydevice.

The illustrated system 10 of FIG. 1 is merely one example. Techniquesfor determining candidates for a candidate list for motion vectorpredictors for a current block may be performed by any digital videoencoding and/or decoding device. Although generally the techniques ofthis disclosure are performed by a video encoding device, the techniquesmay also be performed by a video encoder/decoder, typically referred toas a “CODEC.” Moreover, the techniques of this disclosure may also beperformed by a video preprocessor. Source device 12 and destinationdevice 14 are merely examples of such coding devices in which sourcedevice 12 generates coded video data for transmission to destinationdevice 14. In some examples, devices 12, 14 may operate in asubstantially symmetrical manner such that each of devices 12, 14include video encoding and decoding components. Hence, system 10 maysupport one-way or two-way video transmission between video devices 12,14, e.g., for video streaming, video playback, video broadcasting, orvideo telephony.

Video source 18 of source device 12 may include a video capture device,such as a video camera, a video archive containing previously capturedvideo, and/or a video feed interface to receive video from a videocontent provider. As a further alternative, video source 18 may generatecomputer graphics-based data as the source video, or a combination oflive video, archived video, and computer-generated video. In some cases,if video source 18 is a video camera, source device 12 and destinationdevice 14 may form so-called camera phones or video phones. As mentionedabove, however, the techniques described in this disclosure may beapplicable to video coding in general, and may be applied to wirelessand/or wired applications. In each case, the captured, pre-captured, orcomputer-generated video may be encoded by video encoder 20. The encodedvideo information may then be output by output interface 22 onto acomputer-readable medium 16.

Computer-readable medium 16 may include transient media, such as awireless broadcast or wired network transmission, or storage media (thatis, non-transitory storage media), such as a hard disk, flash drive,compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. In some examples, a network server (not shown)may receive encoded video data from source device 12 and provide theencoded video data to destination device 14, e.g., via networktransmission, direct wired communication, etc. Similarly, a computingdevice of a medium production facility, such as a disc stampingfacility, may receive encoded video data from source device 12 andproduce a disc containing the encoded video data. Therefore,computer-readable medium 16 may be understood to include one or morecomputer-readable media of various forms, in various examples.

Input interface 28 of destination device 14 receives information fromcomputer-readable medium 16. The information of computer-readable medium16 may include syntax information defined by video encoder 20, which isalso used by video decoder 30, that includes syntax elements thatdescribe characteristics and/or processing of blocks and other codedunits, e.g., GOPs. Display device 32 displays the decoded video data toa user, and may comprise any of a variety of display devices such as acathode ray tube (CRT), a liquid crystal display (LCD), a plasmadisplay, an organic light emitting diode (OLED) display, or another typeof display device.

Video encoder 20 and video decoder 30 may operate according to a videocoding standard, such as the High Efficiency Video Coding (HEVC)standard presently under development, and may conform to the HEVC TestModel (HM). Alternatively, video encoder 20 and video decoder 30 mayoperate according to other proprietary or industry standards, such asthe ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10,Advanced Video Coding (AVC), or extensions of such standards. Thetechniques of this disclosure, however, are not limited to anyparticular coding standard, including but not limited to any of thestandards listed above. Other examples of video coding standards includeMPEG-2 and ITU-T H.263. Although not shown in FIG. 1, in some aspects,video encoder 20 and video decoder 30 may each be integrated with anaudio encoder and decoder, and may include appropriate MUX-DEMUX units,or other hardware and software, to handle encoding of both audio andvideo in a common data stream or separate data streams. If applicable,MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, orother protocols such as the user datagram protocol (UDP).

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of video encoder 20 and video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder (CODEC) in a respectivedevice. A device including video encoder 20 and/or video decoder 30 maycomprise an integrated circuit, a microprocessor, and/or a wirelesscommunication device, such as a cellular telephone.

The JCT-VC is working on development of the HEVC standard. The HEVCstandardization efforts are based on an evolving model of a video codingdevice referred to as the HEVC Test Model (HM). The HM presumes severaladditional capabilities of video coding devices relative to existingdevices according to, e.g., ITU-T H.264/AVC. For example, whereas H.264provides nine intra-prediction encoding modes, the HM may provide asmany as thirty-three intra-prediction encoding modes.

In general, the working model of the HM describes that a video frame orpicture may be divided into a sequence of treeblocks or largest codingunits (LCU) that include both luma and chroma samples. Syntax datawithin a bitstream may define a size for the LCU, which is a largestcoding unit in terms of the number of pixels. A slice includes a numberof consecutive treeblocks in coding order. A video frame or picture maybe partitioned into one or more slices. Each treeblock may be split intocoding units (CUs) according to a quadtree. In general, a quadtree datastructure includes one node per CU, with a root node corresponding tothe treeblock. If a CU is split into four sub-CUs, the nodecorresponding to the CU includes four leaf nodes, each of whichcorresponds to one of the sub-CUs.

Each node of the quadtree data structure may provide syntax data for thecorresponding CU. For example, a node in the quadtree may include asplit flag, indicating whether the CU corresponding to the node is splitinto sub-CUs. Syntax elements for a CU may be defined recursively, andmay depend on whether the CU is split into sub-CUs. If a CU is not splitfurther, it is referred as a leaf-CU. In this disclosure, four sub-CUsof a leaf-CU will also be referred to as leaf-CUs even if there is noexplicit splitting of the original leaf-CU. For example, if a CU at16×16 size is not split further, the four 8×8 sub-CUs will also bereferred to as leaf-CUs although the 16×16 CU was never split.

A CU has a similar purpose as a macroblock of the H.264 standard, exceptthat a CU does not have a size distinction. For example, a treeblock maybe split into four child nodes (also referred to as sub-CUs), and eachchild node may in turn be a parent node and be split into another fourchild nodes. A final, unsplit child node, referred to as a leaf node ofthe quadtree, comprises a coding node, also referred to as a leaf-CU.Syntax data associated with a coded bitstream may define a maximumnumber of times a treeblock may be split, referred to as a maximum CUdepth, and may also define a minimum size of the coding nodes.Accordingly, a bitstream may also define a smallest coding unit (SCU).This disclosure uses the term “block” to refer to any of a CU, PU, orTU, in the context of HEVC, or similar data structures in the context ofother standards (e.g., macroblocks and sub-blocks thereof in H.264/AVC).

A CU includes a coding node and prediction units (PUs) and transformunits (TUs) associated with the coding node. A size of the CUcorresponds to a size of the coding node and must be square in shape.The size of the CU may range from 8×8 pixels up to the size of thetreeblock with a maximum of 64×64 pixels or greater. Each CU may containone or more PUs and one or more TUs. Syntax data associated with a CUmay describe, for example, partitioning of the CU into one or more PUs.Partitioning modes may differ between whether the CU is skip or directmode encoded, intra-prediction mode encoded, or inter-prediction modeencoded. PUs may be partitioned to be non-square in shape. Syntax dataassociated with a CU may also describe, for example, partitioning of theCU into one or more TUs according to a quadtree. A TU can be square ornon-square (e.g., rectangular) in shape.

The HEVC standard allows for transformations according to TUs, which maybe different for different CUs. The TUs are typically sized based on thesize of PUs within a given CU defined for a partitioned LCU, althoughthis may not always be the case. The TUs are typically the same size orsmaller than the PUs. In some examples, residual samples correspondingto a CU may be subdivided into smaller units using a quadtree structureknown as “residual quad tree” (RQT). The leaf nodes of the RQT may bereferred to as transform units (TUs). Pixel difference values associatedwith the TUs may be transformed to produce transform coefficients, whichmay be quantized.

A leaf-CU may include one or more prediction units (PUs). In general, aPU represents a spatial area corresponding to all or a portion of thecorresponding CU, and may include data for retrieving a reference samplefor the PU. Moreover, a PU includes data related to prediction. Forexample, when the PU is intra-mode encoded, data for the PU may beincluded in a residual quadtree (RQT), which may include data describingan intra-prediction mode for a TU corresponding to the PU. As anotherexample, when the PU is inter-mode encoded, the PU may include datadefining one or more motion vectors for the PU. The data defining themotion vector for a PU may describe, for example, a horizontal componentof the motion vector, a vertical component of the motion vector, aresolution for the motion vector (e.g., one-quarter pixel precision orone-eighth pixel precision), a reference picture to which the motionvector points, and/or a reference picture list (e.g., List 0, List 1, orList C) for the motion vector.

A leaf-CU having one or more PUs may also include one or more transformunits (TUs). The transform units may be specified using an RQT (alsoreferred to as a TU quadtree structure), as discussed above. Forexample, a split flag may indicate whether a leaf-CU is split into fourtransform units. Then, each transform unit may be split further intofurther sub-TUs. When a TU is not split further, it may be referred toas a leaf-TU. Generally, for intra coding, all the leaf-TUs belonging toa leaf-CU share the same intra prediction mode. That is, the sameintra-prediction mode is generally applied to calculate predicted valuesfor all TUs of a leaf-CU. For intra coding, a video encoder maycalculate a residual value for each leaf-TU using the intra predictionmode, as a difference between the portion of the CU corresponding to theTU and the original block. A TU is not necessarily limited to the sizeof a PU. Thus, TUs may be larger or smaller than a PU. For intra coding,a PU may be collocated with a corresponding leaf-TU for the same CU. Insome examples, the maximum size of a leaf-TU may correspond to the sizeof the corresponding leaf-CU.

Moreover, TUs of leaf-CUs may also be associated with respectivequadtree data structures, referred to as residual quadtrees (RQTs). Thatis, a leaf-CU may include a quadtree indicating how the leaf-CU ispartitioned into TUs. The root node of a TU quadtree generallycorresponds to a leaf-CU, while the root node of a CU quadtree generallycorresponds to a treeblock (or LCU). TUs of the RQT that are not splitare referred to as leaf-TUs. In general, this disclosure uses the termsCU and TU to refer to leaf-CU and leaf-TU, respectively, unless notedotherwise.

A video sequence typically includes a series of video frames orpictures. A group of pictures (GOP) generally comprises a series of oneor more of the video pictures. A GOP may include syntax data in a headerof the GOP, a header of one or more of the pictures, or elsewhere, thatdescribes a number of pictures included in the GOP. Each slice of apicture may include slice syntax data that describes an encoding modefor the respective slice. Video encoder 20 typically operates on videoblocks within individual video slices in order to encode the video data.A video block may correspond to a coding node within a CU. The videoblocks may have fixed or varying sizes, and may differ in size accordingto a specified coding standard.

As an example, the HM supports prediction in various PU sizes. Assumingthat the size of a particular CU is 2N×2N, the HM supportsintra-prediction in PU sizes of 2N×2N or N×N, and inter-prediction insymmetric PU sizes of 2N×2N, 2N×N, N×2N, or N×N. The HM also supportsasymmetric partitioning for inter-prediction in PU sizes of 2N×nU,2N×nD, nL×2N, and nR×2N. In asymmetric partitioning, one direction of aCU is not partitioned, while the other direction is partitioned into 25%and 75%. The portion of the CU corresponding to the 25% partition isindicated by an “n” followed by an indication of “Up,” “Down,” “Left,”or “Right.” Thus, for example, “2N×nU” refers to a 2N×2N CU that ispartitioned horizontally with a 2N×0.5N PU on top and a 2N×1.5N PU onbottom.

In this disclosure, “N×N” and “N by N” may be used interchangeably torefer to the pixel dimensions of a video block in terms of vertical andhorizontal dimensions, e.g., 16×16 pixels or 16 by 16 pixels. Ingeneral, a 16×16 block will have 16 pixels in a vertical direction(y=16) and 16 pixels in a horizontal direction (x=16). Likewise, an N×Nblock generally has N pixels in a vertical direction and N pixels in ahorizontal direction, where N represents a nonnegative integer value.The pixels in a block may be arranged in rows and columns. Moreover,blocks need not necessarily have the same number of pixels in thehorizontal direction as in the vertical direction. For example, blocksmay comprise N×M pixels, where M is not necessarily equal to N.

Following intra-predictive or inter-predictive coding using the PUs of aCU, video encoder 20 may calculate residual data for the TUs of the CU.The PUs may comprise syntax data describing a method or mode ofgenerating predictive pixel data in the spatial domain (also referred toas the pixel domain) and the TUs may comprise coefficients in thetransform domain following application of a transform, e.g., a discretecosine transform (DCT), an integer transform, a wavelet transform, or aconceptually similar transform to residual video data. The residual datamay correspond to pixel differences between pixels of the unencodedpicture and prediction values corresponding to the PUs. Video encoder 20may form the TUs including the residual data for the CU, and thentransform the TUs to produce transform coefficients for the CU.

Following any transforms to produce transform coefficients, videoencoder 20 may perform quantization of the transform coefficients.Quantization generally refers to a process in which transformcoefficients are quantized to possibly reduce the amount of data used torepresent the coefficients, providing further compression. Thequantization process may reduce the bit depth associated with some orall of the coefficients. For example, an n-bit value may be rounded downto an m-bit value during quantization, where n is greater than m.

Following quantization, the video encoder may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) coefficients at the front of the array and to place lowerenergy (and therefore higher frequency) coefficients at the back of thearray. In some examples, video encoder 20 may utilize a predefined scanorder to scan the quantized transform coefficients to produce aserialized vector that can be entropy encoded. In other examples, videoencoder 20 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form a one-dimensional vector, video encoder20 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive variable length coding (CAVLC), context-adaptive binaryarithmetic coding (CABAC), syntax-based context-adaptive binaryarithmetic coding (SBAC), Probability Interval Partitioning Entropy(PIPE) coding or another entropy encoding methodology. Video encoder 20may also entropy encode syntax elements associated with the encodedvideo data for use by video decoder 30 in decoding the video data.

To perform CABAC, video encoder 20 may assign a context within a contextmodel to a symbol to be transmitted. The context may relate to, forexample, whether neighboring values of the symbol are non-zero or not.To perform CAVLC, video encoder 20 may select a variable length code fora symbol to be transmitted. Codewords in VLC may be constructed suchthat relatively shorter codes correspond to more probable symbols, whilelonger codes correspond to less probable symbols. In this way, the useof VLC may achieve a bit savings over, for example, using equal-lengthcodewords for each symbol to be transmitted. The probabilitydetermination may be based on a context assigned to the symbol.

Video encoder 20 may further send syntax data, such as block-basedsyntax data, frame-based syntax data, and GOP-based syntax data, tovideo decoder 30, e.g., in a frame header, a block header, a sliceheader, or a GOP header. The GOP syntax data may describe a number offrames in the respective GOP, and the frame syntax data may indicate anencoding/prediction mode used to encode the corresponding frame.

FIG. 2 is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure. Video encoder 20 may be configured to perform any orall of the techniques of this disclosure. As one example, mode selectunit 40 may be configured to perform any or all of the techniquesdescribed in this disclosure. However, aspects of this disclosure arenot so limited. In some examples, the techniques described in thisdisclosure may be shared among the various components of video encoder20. In some examples, in addition to or instead of, a processor (notshown) may be configured to perform any or all of the techniquesdescribed in this disclosure.

In some embodiments, the mode select unit 40, the motion estimation unit42, the motion compensation unit 44 (or another component of the modeselect unit 40, shown or not shown), or another component of the encoder20 (shown or not shown) may perform the techniques of this disclosure.For example, the mode select unit 40 may receive video data forencoding, which may be encoded into a base layer and corresponding oneor more enhancement layers. The mode select unit 40, the motionestimation unit 42, the motion compensation unit 44, or anotherappropriate unit of the encoder 20 may determine pixel accuracy ofmotion predictor information. The appropriate unit of the encoder 20 candetermine a motion vector based on the pixel accuracy of the motionpredictor information, and determine a value of a video unit based atleast in part on the motion vector. The encoder 20 can encode the videounit and signal the motion predictor information in a bitstream.

Video encoder 20 may perform intra- and inter-coding of video blockswithin video slices. Intra-coding relies on spatial prediction to reduceor remove spatial redundancy in video within a given video frame orpicture. Inter-coding relies on temporal prediction to reduce or removetemporal redundancy in video within adjacent frames or pictures of avideo sequence. Intra-mode (I mode) may refer to any of several spatialbased coding modes. Inter-modes, such as uni-directional prediction (Pmode) or bi-prediction (B mode), may refer to any of severaltemporal-based coding modes.

As shown in FIG. 2, video encoder 20 receives a current video blockwithin a video frame to be encoded. In the example of FIG. 1, videoencoder 20 includes mode select unit 40, reference frame memory 64,summer 50, transform processing unit 52, quantization unit 54, andentropy encoding unit 56. Mode select unit 40, in turn, includes motioncompensation unit 44, motion estimation unit 42, intra-prediction unit46, and partition unit 48. For video block reconstruction, video encoder20 also includes inverse quantization unit 58, inverse transform unit60, and summer 62. A deblocking filter (not shown in FIG. 2) may also beincluded to filter block boundaries to remove blockiness artifacts fromreconstructed video. If desired, the deblocking filter would typicallyfilter the output of summer 62. Additional filters (in loop or postloop) may also be used in addition to the deblocking filter. Suchfilters are not shown for brevity, but if desired, may filter the outputof summer 50 (as an in-loop filter).

During the encoding process, video encoder 20 receives a video frame orslice to be coded. The frame or slice may be divided into multiple videoblocks. Motion estimation unit 42 and motion compensation unit 44perform inter-predictive coding of the received video block relative toone or more blocks in one or more reference frames to provide temporalprediction. Intra-prediction unit 46 may alternatively performintra-predictive coding of the received video block relative to one ormore neighboring blocks in the same frame or slice as the block to becoded to provide spatial prediction. Video encoder 20 may performmultiple coding passes, e.g., to select an appropriate coding mode foreach block of video data.

Moreover, partition unit 48 may partition blocks of video data intosub-blocks, based on evaluation of previous partitioning schemes inprevious coding passes. For example, partition unit 48 may initiallypartition a frame or slice into LCUs, and partition each of the LCUsinto sub-CUs based on rate-distortion analysis (e.g., rate-distortionoptimization). Mode select unit 40 may further produce a quadtree datastructure indicative of partitioning of an LCU into sub-CUs. Leaf-nodeCUs of the quadtree may include one or more PUs and one or more TUs.

Mode select unit 40 may select one of the coding modes, intra or inter,e.g., based on error results, and provides the resulting intra- orinter-coded block to summer 50 to generate residual block data and tosummer 62 to reconstruct the encoded block for use as a reference frame.Mode select unit 40 also provides syntax elements, such as motionvectors, intra-mode indicators, partition information, and other suchsyntax information, to entropy encoding unit 56.

Motion estimation unit 42 and motion compensation unit 44 may be highlyintegrated, but are illustrated separately for conceptual purposes.Motion estimation, performed by motion estimation unit 42, is theprocess of generating motion vectors, which estimate motion for videoblocks. A motion vector, for example, may indicate the displacement of aPU of a video block within a current video frame or picture relative toa predictive block within a reference frame (or other coded unit)relative to the current block being coded within the current frame (orother coded unit). A predictive block is a block that is found toclosely match the block to be coded, in terms of pixel difference, whichmay be determined by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics. In some examples, videoencoder 20 may calculate values for sub-integer pixel positions ofreference pictures stored in reference frame memory 64. For example,video encoder 20 may interpolate values of one-quarter pixel positions,one-eighth pixel positions, or other fractional pixel positions of thereference picture. Therefore, motion estimation unit 42 may perform amotion search relative to the full pixel positions and fractional pixelpositions and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. The referencepicture may be selected from a first reference picture list (List 0) ora second reference picture list (List 1), each of which identify one ormore reference pictures stored in reference frame memory 64. Motionestimation unit 42 sends the calculated motion vector to entropyencoding unit 56 and motion compensation unit 44.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation unit 42. Again, motion estimationunit 42 and motion compensation unit 44 may be functionally integrated,in some examples. Upon receiving the motion vector for the PU of thecurrent video block, motion compensation unit 44 may locate thepredictive block to which the motion vector points in one of thereference picture lists. Summer 50 forms a residual video block bysubtracting pixel values of the predictive block from the pixel valuesof the current video block being coded, forming pixel difference values,as discussed below. In general, motion estimation unit 42 performsmotion estimation relative to luma components, and motion compensationunit 44 uses motion vectors calculated based on the luma components forboth chroma components and luma components. Mode select unit 40 may alsogenerate syntax elements associated with the video blocks and the videoslice for use by video decoder 30 in decoding the video blocks of thevideo slice.

Intra-prediction unit 46 may intra-predict a current block, as analternative to the inter-prediction performed by motion estimation unit42 and motion compensation unit 44, as described above. In particular,intra-prediction unit 46 may determine an intra-prediction mode to useto encode a current block. In some examples, intra-prediction unit 46may encode a current block using various intra-prediction modes, e.g.,during separate encoding passes, and intra-prediction unit 46 (or modeselect unit 40, in some examples) may select an appropriateintra-prediction mode to use from the tested modes.

For example, intra-prediction unit 46 may calculate rate-distortionvalues using a rate-distortion analysis for the various testedintra-prediction modes, and select the intra-prediction mode having thebest rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bitrate(that is, a number of bits) used to produce the encoded block.Intra-prediction unit 46 may calculate ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block.

After selecting an intra-prediction mode for a block, intra-predictionunit 46 may provide information indicative of the selectedintra-prediction mode for the block to entropy encoding unit 56. Entropyencoding unit 56 may encode the information indicating the selectedintra-prediction mode. Video encoder 20 may include in the transmittedbitstream configuration data, which may include a plurality ofintra-prediction mode index tables and a plurality of modifiedintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks, andindications of a most probable intra-prediction mode, anintra-prediction mode index table, and a modified intra-prediction modeindex table to use for each of the contexts.

Video encoder 20 forms a residual video block by subtracting theprediction data from mode select unit 40 from the original video blockbeing coded. Summer 50 represents the component or components thatperform this subtraction operation. Transform processing unit 52 appliesa transform, such as a discrete cosine transform (DCT) or a conceptuallysimilar transform, to the residual block, producing a video blockcomprising residual transform coefficient values. Transform processingunit 52 may perform other transforms which are conceptually similar toDCT. Wavelet transforms, integer transforms, sub-band transforms orother types of transforms could also be used. In any case, transformprocessing unit 52 applies the transform to the residual block,producing a block of residual transform coefficients. The transform mayconvert the residual information from a pixel value domain to atransform domain, such as a frequency domain. Transform processing unit52 may send the resulting transform coefficients to quantization unit54. Quantization unit 54 quantizes the transform coefficients to furtherreduce bit rate. The quantization process may reduce the bit depthassociated with some or all of the coefficients. The degree ofquantization may be modified by adjusting a quantization parameter. Insome examples, quantization unit 54 may then perform a scan of thematrix including the quantized transform coefficients. Alternatively,entropy encoding unit 56 may perform the scan.

Following quantization, entropy encoding unit 56 entropy codes thequantized transform coefficients. For example, entropy encoding unit 56may perform context adaptive variable length coding (CAVLC), contextadaptive binary arithmetic coding (CABAC), syntax-based context-adaptivebinary arithmetic coding (SBAC), probability interval partitioningentropy (PIPE) coding or another entropy coding technique. In the caseof context-based entropy coding, context may be based on neighboringblocks. Following the entropy coding by entropy encoding unit 56, theencoded bitstream may be transmitted to another device (e.g., videodecoder 30) or archived for later transmission or retrieval.

Inverse quantization unit 58 and inverse transform unit 60 apply inversequantization and inverse transformation, respectively, to reconstructthe residual block in the pixel domain, e.g., for later use as areference block. Motion compensation unit 44 may calculate a referenceblock by adding the residual block to a predictive block of one of theframes of reference frame memory 64. Motion compensation unit 44 mayalso apply one or more interpolation filters to the reconstructedresidual block to calculate sub-integer pixel values for use in motionestimation. Summer 62 adds the reconstructed residual block to themotion compensated prediction block produced by motion compensation unit44 to produce a reconstructed video block for storage in reference framememory 64. The reconstructed video block may be used by motionestimation unit 42 and motion compensation unit 44 as a reference blockto inter-code a block in a subsequent video frame.

FIG. 3 is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure. Video decoder 30 may be configured to perform any orall of the techniques of this disclosure. As one example, motioncompensation unit 72 and/or intra prediction unit 74 may be configuredto perform any or all of the techniques described in this disclosure.However, aspects of this disclosure are not so limited. In someexamples, the techniques described in this disclosure may be sharedamong the various components of video decoder 30. In some examples, inaddition to or instead of, a processor (not shown) may be configured toperform any or all of the techniques described in this disclosure.

In some embodiments, the entropy decoding unit 70, the motioncompensation unit 72, or another component of the decoder 30 (shown ornot shown) may perform the techniques of this disclosure. The motioncompensation unit 72 or another appropriate unit of the decoder 30 maydetermine pixel accuracy of motion predictor information. Theappropriate unit of the decoder 30 can determine a motion vector basedon the pixel accuracy of the motion predictor information, and determinea value of a video unit based at least in part on the motion vector. Thedecoder 30 can decode the video unit and receive the motion predictorinformation in a bitstream.

In the example of FIG. 3, video decoder 30 includes an entropy decodingunit 70, motion compensation unit 72, intra prediction unit 74, inversequantization unit 76, inverse transformation unit 78, reference framememory 82 and summer 80. Video decoder 30 may, in some examples, performa decoding pass generally reciprocal to the encoding pass described withrespect to video encoder 20 (FIG. 2). Motion compensation unit 72 maygenerate prediction data based on motion vectors received from entropydecoding unit 70, while intra-prediction unit 74 may generate predictiondata based on intra-prediction mode indicators received from entropydecoding unit 70.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video slice andassociated syntax elements from video encoder 20. Entropy decoding unit70 of video decoder 30 entropy decodes the bitstream to generatequantized coefficients, motion vectors or intra-prediction modeindicators, and other syntax elements. Entropy decoding unit 70 forwardsthe motion vectors to and other syntax elements to motion compensationunit 72. Video decoder 30 may receive the syntax elements at the videoslice level and/or the video block level.

When the video slice is coded as an intra-coded (I) slice, intraprediction unit 74 may generate prediction data for a video block of thecurrent video slice based on a signaled intra prediction mode and datafrom previously decoded blocks of the current frame or picture. When thevideo frame is coded as an inter-coded (e.g., B, P or GPB) slice, motioncompensation unit 72 produces predictive blocks for a video block of thecurrent video slice based on the motion vectors and other syntaxelements received from entropy decoding unit 70. The predictive blocksmay be produced from one of the reference pictures within one of thereference picture lists. Video decoder 30 may construct the referenceframe lists, List 0 and List 1, using default construction techniquesbased on reference pictures stored in reference frame memory 92. Motioncompensation unit 72 determines prediction information for a video blockof the current video slice by parsing the motion vectors and othersyntax elements, and uses the prediction information to produce thepredictive blocks for the current video block being decoded. Forexample, motion compensation unit 72 uses some of the received syntaxelements to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice, P slice, or GPB slice),construction information for one or more of the reference picture listsfor the slice, motion vectors for each inter-encoded video block of theslice, inter-prediction status for each inter-coded video block of theslice, and other information to decode the video blocks in the currentvideo slice.

Motion compensation unit 72 may also perform interpolation based oninterpolation filters. Motion compensation unit 72 may use interpolationfilters as used by video encoder 20 during encoding of the video blocksto calculate interpolated values for sub-integer pixels of referenceblocks. In this case, motion compensation unit 72 may determine theinterpolation filters used by video encoder 20 from the received syntaxelements and use the interpolation filters to produce predictive blocks.

Inverse quantization unit 76 inverse quantizes, e.g., de-quantizes, thequantized transform coefficients provided in the bitstream and decodedby entropy decoding unit 80. The inverse quantization process mayinclude use of a quantization parameter QPy calculated by video decoder30 for each video block in the video slice to determine a degree ofquantization and, likewise, a degree of inverse quantization that shouldbe applied.

Inverse transform unit 78 applies an inverse transform, e.g., an inverseDCT, an inverse integer transform, or a conceptually similar inversetransform process, to the transform coefficients in order to produceresidual blocks in the pixel domain.

After motion compensation unit 82 generates the predictive block for thecurrent video block based on the motion vectors and other syntaxelements, video decoder 30 forms a decoded video block by summing theresidual blocks from inverse transform unit 78 with the correspondingpredictive blocks generated by motion compensation unit 72. Summer 90represents the component or components that perform this summationoperation. If desired, a deblocking filter may also be applied to filterthe decoded blocks in order to remove blockiness artifacts. Other loopfilters (either in the coding loop or after the coding loop) may also beused to smooth pixel transitions, or otherwise improve the videoquality. The decoded video blocks in a given frame or picture are thenstored in reference picture memory 92, which stores reference picturesused for subsequent motion compensation. Reference frame memory 82 alsostores decoded video for later presentation on a display device, such asdisplay device 32 of FIG. 1.

FIG. 4 is a flowchart illustrating an example method for motion vectordifference coding for enhancement layer according to aspects of thisdisclosure. As explained above, the motion vector characteristics may bedifferent in the difference domain and the non-difference domain (e.g.,pixel domain, etc.). For example, the difference domain is more likelyto contain half-pixel motion vectors, whereas the non-difference domainis more likely to contain quarter-pixel motion vectors. Accordingly, themotion vectors may have varying sub-pixel level accuracy in interprediction in the difference and the non-difference domains. Therefore,it would be advantageous to utilize the motion vector predictorinformation in coding the motion vector delta for the current pixel inthe difference domain.

The example method for motion vector difference coding for enhancementlayer according to aspects of this disclosure uses the motion vectorpredictor information in order to code the motion vector delta for thecurrent prediction unit (PU). The motion vector predictor informationmay include information relating to the motion vectors that are to beused in predicting the value of the current PU. Such information mayinclude the pixel accuracy for the motion vectors. The informationprovided in the motion vector predictor information may be used inpredicting the current PU using the motion vector delta. In interprediction, video units that have temporal correlation (e.g., framesfrom two different points in time) may be used to predict the value ofthe current pixel. The difference between the reference video unit andthe current video unit may be indicated by motion vectors. In HEVC,motion vector information is coded using motion vector deltas, whichindicate the difference between the motion vector of the reference pixeland the motion vector of the current pixel.

The information provided in the motion vector predictor information,such as the pixel accuracy of the reference motion vectors, may be usedto code the motion vector delta for the current video unit moreefficiently. For example, if a predictor motion vector is a quarterpixel, less weight may be given to this predictor motion vector since amotion vector in the difference domain is likely to be a half pixel. Onthe other hand, if a predictor motion vector is a half pixel, moreweight may be given to the prediction motion vector since a motionvector in the difference domain is likely to be a half pixel. Similarly,if a predictor motion vector is from the non-difference domain, it maybe given less weight in predicting the value of the current pixel in thedifference domain. On the other hand, if the predictor motion vector isfrom the difference domain, it may be given more weight.

In the current implementation of HEVC, the motion vector predictorinformation is coded after the motion vector delta. Accordingly, themotion vector predictor information is not used in processing the motionvector delta. The example method for motion difference coding accordingto aspects of this disclosure may change the coding order such that themotion vector predictor information is available prior to coding themotion vector delta. For example, the current syntax for motion vectorcoding in HEVC is as follows:

-   -   Ref_Idx    -   Mvd_coding    -   MVP_index        The “Ref_Idx” flag refers to the temporal references. Multiple        temporal references may be used. Temporal references are the        references at different points in time, from which the motion        vectors for calculating the current pixel value will be        obtained. The “Mvd_coding” flag refers to motion vector delta,        which is the difference between the predictor motion vector and        the current (or actual) motion vector. The “MVP_index” refers to        motion vector predictor information, which indicates the motion        vectors from the pixels that are close to the current pixel. In        some embodiments, the coding order of the syntax may be changed        as follows:    -   Ref_Idx    -   MVP_index    -   Mvd_coding

By coding the motion vector predictor information prior to coding themotion vector delta information, the predictor information may beavailable in coding the motion vector. For example, the encoder ordecoder may adjust the process of predicting the value of the currentpixel in the difference domain depending on the pixel accuracy in themotion vector predictor information. Such adjustment may includeincreasing, decreasing, multiplying, or dividing the value of thecurrent pixel by a coefficient. Accordingly, the example method formotion vector difference coding may incorporate the characteristics andstatistics of motion vectors in the difference domain and thenon-difference domain in order to code the motion vector delta for thepixels in the difference domain. In some embodiments, the syntax formotion vector difference coding may be modified as follows:

TABLE 1 Example PU Level Inter Mode Syntax Information Decoding forEnhancement Layer MODE_INTER */ merge_flag[x0][y0] if(merge_flag[x0][y0]) { if (MaxNumMergeCand > 1) merge_idx[x0][y0] } else{ if (slice_type = = B) inter_pred_flag[x0][y0] if(inter_pred_flag[x0][y0] = = Pred_LC) { if(num_ref_idx_lc_active_minus1 > 0) ref_idx_lc[x0][y0]mvp_lc_flag[x0][y0] mvd_coding(mvd_lc[x0][y0][0], mvd_lc[x0][y0][1]) }else { /* Pred_L0 or Pred_Bl */ if (num_ref_idx_l0_active_minus1 > 0)ef_idx_l0[x0][y0] mvp_l0_flag[x0][y0] mvd_coding(mvd_l0[x0][y0][0],mvd_l0[x0][y0][1]) } if (inter_pred_flag[x0][y0] = = Pred_Bl) { if(num_ref_idx_l1_active_minus1 > 0) ref_idx_l1[x0][y0] if(mvd_l1_zero_flag) { mvd_l1[x0][y0][0] = 0 mvd_l1[x0][y0][1] = 0 } elsemvp_l1_flag[x0][y0] mvd_coding(mvd_l1[x0][y0][0], mvd_l1[x0][y0][1]) } }}In this manner, using motion vector predictor information in order tocode the motion vector delta may lead to better coding efficiency,compression, performance, and quality of video information.

The example method for motion vector difference coding for enhancementlayer according to aspects of this disclosure will now be described indetail with respect to FIG. 4. The process 400 may be performed by anencoder (e.g., the encoder as shown in FIG. 2, etc.) or a decoder (e.g.,the decoder as shown in FIG. 3, etc.). The blocks of the process 400 aredescribed with respect to the encoder 20 in FIG. 2, but the process 400may be performed by other components, such as a decoder, as mentionedabove.

At block 401, the encoder 20 receives temporal reference information forthe current pixel. The temporal reference information may indicatereference frames from different points in time from which the motionvectors for inter prediction may be obtained. The encoder 20 may obtainthe temporal reference information, e.g., by decoding the syntaxinformation. At block 402, the encoder 20 receives motion vectorpredictor information. The encoder 20 may obtain the motion vectorpredictor information, e.g., by decoding the syntax information. Themotion vector predictor information may indicate the location of motionvectors within the temporal references, e.g., where the predictor motionvectors may be found within the reference frames. At block 403, theencoder 20 processes the motion vector delta of the current pixel in thedifference domain based on the pixel accuracy of the predictor motionvector(s). Such processing may include coding the motion vector deltafor the current pixel based on the predictor motion vector(s). Theencoder 20 may give more weight to motion vectors that have a similarpixel type as the current pixel. The encoder 20 may adjust the processof coding the motion vector delta for the current unit appropriatelybased on the information included in the motion vector predictorinformation. Although the example method has been described in terms ofpixels, the example method described with respect to FIG. 4 may beimplemented at various syntax levels. In addition, all embodimentsdescribed with respect to FIG. 4 may be implemented separately, or incombination with one another.

FIG. 4A is a flowchart illustrating another example method for motionvector difference coding for enhancement layer according to aspects ofthis disclosure. The process 400A may be performed by an encoder (e.g.,the encoder as shown in FIG. 2, etc.) or a decoder (e.g., the decoder asshown in FIG. 3, etc.). The blocks of the process 400A are describedwith respect to the encoder 20 in FIG. 2, but the process 400A may beperformed by other components, such as a decoder, as mentioned above.The process 400A may be used to code a video unit in the differencedomain. All embodiments described with respect to FIG. 4A may beimplemented separately, or in combination with one another.

At block 401A, the encoder 20 determines the pixel accuracy of motionpredictor information. Pixel accuracy may refer to accuracy of motionpredictor information. For example, pixel accuracy may indicate theextent to which the motion predictor information is accurate, e.g., themotion predictor information may be accurate to a half-pixel level or aquarter-pixel level, or an even smaller sub-pixel level. Pixel accuracymay also be referred to as “pixel type.” In some embodiments, the motionpredictor information may be motion vector predictor information. Motionvector predictor information may be used in determining the motionvector for the current video unit. The motion vector predictorinformation may include information relating to the motion vectors thatare to be used in predicting the value of the current video unit. Forexample, the motion vector predictor information may provide motionvector candidates for determining the motion vector for the currentvideo unit.

At block 402A, the encoder 20 determines a motion vector based on thepixel accuracy of the motion predictor information. A motion vector maybe used in inter prediction for a video unit. A motion vector may beused to generate a prediction unit for a video unit. The encoder 20 maydetermine the motion vector based on the pixel accuracy of the motionpredictor information. For example, the encoder 20 can choose to use themotion predictor information in determining the motion vector for acurrent video unit if the pixel accuracy meets certain criteria. Suchcriteria may include whether the pixel accuracy is of a type that islikely to occur in the difference domain. In the difference domain,motion vectors may be more likely to have half pixel accuracy.Therefore, in some embodiments where the difference domain is used, theencoder 20 may choose to use the motion predictor information todetermine the motion vector if the pixel accuracy of the motionpredictor information is half pixel. The encoder 20 may choose to notuse motion predictor information with pixel accuracy that does not meetthe desired criteria. The encoder 20 may choose to weight the motionpredictor information (e.g., apply a weighting factor) if the motionpredictor information is not of desired accuracy. Such weighting may bebased on the extent to which the accuracy of the motion predictorinformation matches the desired level of accuracy.

At block 403A, the encoder 20 determines a value of a video unit basedat least in part on the motion vector. A video unit may be any unit ofvideo data, and can include but is not limited to: a frame, a slice, alargest coding unit (LCU), a coding unit (CU), a block, a pixel, and asub-pixel. The value of the video unit may be determined by generating aprediction unit (PU) for the video unit.

In some embodiments, the motion predictor information is the motionvector predictor information, and the encoder 20 determines the motionvector for the current video unit based on the motion vector predictorinformation, motion vector delta, and reference information associatedwith reference video units for the video unit. In one embodiment, thereference information associated with the reference video units is thereference index. The reference index refers to temporal references,which are references at different points in time, from which the motionvector predictor information for the current video unit can be obtained.Motion vector predictors can be obtained from the motion vectorpredictor information for the temporal references indicated by thereference index. The motion vector predictors may or may not be used inpredicting the motion vector for the current video unit depending on thepixel accuracy of the motion vector predictors. The motion vector forthe current video unit may be determined by adding the motion vectordelta to the motion vector predictors.

In certain embodiments, the encoder 20 may also use the motion vectorpredictor information in order to determine the context for codingmotion vector delta.

FIG. 5 is a flowchart illustrating an example method for contextmodeling in the enhancement layer coding according to aspects of thisdisclosure. The motion vector predictor information may be used to codeadditional context information used in entropy coding, e.g.,context-adaptive binary arithmetic coding (CABAC). Context informationmay indicate the probability associated with a value being entropycoded. For example, the context information may indicate the probabilityof the entropy coded value being 1, or the probability of the entropycoded value being 0, etc. In the example method for context modeling theenhancement layer coding, the following contexts are proposed for codingthe motion vector delta syntax:

-   -   “abs_mvd_greater0_flag_Ctx0” and “abs_mvd_greater0_flag_Ctx1”        context for coding horizontal and vertical of        “abs_mvd_greater0_flag”    -   “abs_mvd_greater1_flag_Ctx0” and “abs_mvd_greater1_flag_Ctx1”        context for coding horizontal and vertical of        “abs_mvd_greater1_flag”

In motion vector difference coding, the “abs_mvd_greater0_flag[compIdx]”flag specifies whether the absolute value of a motion vector componentdifference is greater than 0. The horizontal motion vector componentdifference is assigned compIdx=0, and the vertical motion vectorcomponent difference is assigned compIdx=1. Similarly, the“abs_mvd_greater1_flag[compIdx]” flag specifies whether the absolutevalue of a motion vector component difference is greater than 1. Thehorizontal motion vector component difference is assigned compIdx=0, andthe vertical motion vector component difference is assigned compIdx=1.

For “abs_mvd_greater0_flag,” the context selection between the contexts“abs_mvd_greater0_flag_Ctx0” and “abs_mvd_greater0_flag_Ctx1” may beperformed as follows:

If (diff_coding_flag && (predictorMV & 0x1)) abs_mvd_greater0_flag_Ctx0Else abs_mvd_greater0_flag_Ctx1For example, in the difference domain, if the predictor motion vector is0, the context is coded as “abs_mvd_greater0_flag_Ctx0.” If thepredictor motion vector is 1, the context is coded as“abs_mvd_greater0_flag_Ctx1.” The expression (predictorMV & 0×1)determines whether the predictor is half-pixel accuracy or quarter-pixelaccuracy. If PredictorMV is odd, it indicates that the predictor isquarter pixel accuracy, and if PredictorMV is even, it indicates thatthe predictor is half pixel accuracy. For “abs_mvd_greater1_flag,” thecontext selection between the contexts “abs_mvd_greater1_flag_Ctx0” and“abs_mvd_greater0_flag_Ctx1” may be performed as follows:

If (diff_coding_flag && (predictorMV & 0x1)) abs_mvd_greater1_flag_Ctx0Else abs_mvd_greater1_flag_Ctx1For example, in the difference domain, if the predictor motion vector is0, the context is coded as “abs_mvd_greater1_flag_Ctx0.” If thepredictor motion vector is 1, the context is coded as“abs_mvd_greater1_flag_Ctx1.” In this manner, additional contextinformation may be provided based on the motion vector predictorinformation. Additional context information may lead to bettercompression, better performance, and quality improvement of videoinformation.

The example method for context modeling for enhancement layer codingaccording to aspects of this disclosure will now be described in detailwith reference to FIG. 5. The process 500 may be performed by an encoder(e.g., the encoder as shown in FIG. 2, etc.) or a decoder (e.g., thedecoder as shown in FIG. 3, etc.). The block of the process 500 aredescribed with respect to the encoder 20 in FIG. 2, but the process 500may be performed by other components, such as a decoder, as mentionedabove.

At block 501, the encoder 20 receives motion vector predictorinformation. For example, the motion vector predictor information may bedecoded from the syntax information. The encoder 20 may determine thepixel type of the motion vectors included in the motion vector predictorinformation. For example, the motion vectors in the motion vectorpredictor information may be half pixels or quarter pixels or evensmaller. At block 502, the encoder 20 determines the context informationfor entropy coding based on the pixel type of the predictor motionvectors. As explained above, additional context information may beprovided in entropy coding based on the type of motion vector. At block503, the encoder 20 codes the context information determined at block502 in entropy coding. Although the example method has been described interms of pixels, the example method described with respect to FIG. 5 maybe implemented at various syntax levels. In addition, all embodimentsdescribed with respect to FIG. 5 may be implemented separately, or incombination with one another.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. An apparatus configured to code videoinformation, the apparatus comprising: a memory unit configured to storedifference video information associated with a difference video layer ofpixel information derived from a difference between an enhancement layerand a corresponding base layer of the video information; and a processorin communication with the memory unit, the processor configured to:determine pixel accuracy of motion predictor information; determine amotion vector based on the pixel accuracy of the motion predictorinformation; and determine a value of a video unit based at least inpart on the motion vector.
 2. The apparatus of claim 1, whereindetermining the value of the video unit comprises performing interprediction for the video unit based on the difference video layer. 3.The apparatus of claim 1, wherein the motion predictor informationcomprises motion vector predictor information.
 4. The apparatus of claim3, wherein the motion vector is determined based on the motion vectorpredictor information, a motion vector delta, and information associatedwith reference video units for the video unit, wherein the motion vectorpredictor information is associated with the reference video units, andthe motion vector is determined by adding the motion vector delta andthe motion vector predictor information.
 5. The apparatus of claim 4,wherein the information associated with the reference video unitscomprises one or more reference indexes.
 6. The apparatus of claim 4,wherein the motion vector predictor information is obtained prior to themotion vector delta.
 7. The apparatus of claim 1, wherein the processoris further configured to determine the motion vector by adding a motionvector delta to the motion predictor information when the pixel accuracyis one that is likely to occur in the difference video layer.
 8. Theapparatus of claim 7, wherein the pixel accuracy is half pixel.
 9. Theapparatus of claim 1, wherein the processor is further configured todetermine the motion vector by adjusting a sum of a motion vector deltaand the motion predictor information based upon the pixel accuracy. 10.The apparatus of claim 9, wherein said adjusting comprises applying aweighting factor to the sum of the motion vector delta and the motionpredictor information based upon the pixel accuracy.
 11. The apparatusof claim 9, wherein said adjusting comprises increasing the sum when thepixel accuracy is likely to occur in the difference video layer.
 12. Theapparatus of claim 11, wherein said adjusting comprises increasing thesum when the pixel accuracy is half pixel.
 13. The apparatus of claim 9,wherein said adjusting comprises decreasing the sum when the pixelaccuracy is unlikely to occur in the difference video layer.
 14. Theapparatus of claim 13, wherein said adjusting comprises decreasing thesum when the pixel accuracy is a quarter pixel or smaller.
 15. Theapparatus of claim 1, wherein the processor is further configured todetermine context information for entropy coding based upon the pixelaccuracy.
 16. The apparatus of claim 15, wherein the processor isfurther configured to determine a context for entropy coding of a motionvector delta based on the pixel accuracy.
 17. The apparatus of claim 1,wherein the video unit is selected from a group comprising: frame,slice, largest coding unit (LCU), coding unit (CU), block, pixel, andsub-pixel.
 18. The apparatus of claim 1, wherein the processor isfurther configured to determine the value of the video unit bygenerating a prediction unit for the video unit.
 19. The apparatus ofclaim 1, wherein the base layer is a reconstructed base layer.
 20. Theapparatus of claim 1, wherein the processor is further configured encodethe video unit and to signal the motion predictor information in abitstream.
 21. The apparatus of claim 1, wherein the processor isfurther configured decode the video unit and to receive the motionpredictor information in a bitstream.
 22. The apparatus of claim 1,wherein the apparatus is selected from a group consisting of one or moreof: a desktop computer, a notebook computer, a laptop computer, a tabletcomputer, a set-top box, a telephone handset, a smart phone, a smartpad, a television, a camera, a display device, a digital media player, avideo gaming console, and a video streaming device.
 23. A method ofcoding video information comprising: storing difference videoinformation associated with a difference video layer of pixelinformation derived from a difference between an enhancement layer and acorresponding base layer of the video information; determining pixelaccuracy of motion predictor information; determining a motion vectorbased on the pixel accuracy of the motion predictor information; anddetermining a value of a video unit based at least in part on the motionvector.
 24. The method of claim 23, wherein determining the value of thevideo unit comprises performing inter prediction for the video unitbased on the difference video layer.
 25. The method of claim 23, whereinthe motion predictor information comprises motion vector predictorinformation.
 26. The method of claim 25, wherein the motion vector isdetermined based on the motion vector predictor information, a motionvector delta, and information associated with reference video units forthe video unit, wherein the motion vector predictor information isassociated with the reference video units, and the motion vector isdetermined by adding the motion vector delta and the motion vectorpredictor information.
 27. The method of claim 26, wherein theinformation associated with the reference video units comprises one ormore reference indexes.
 28. The method of claim 26, wherein the motionvector predictor information is obtained prior to the motion vectordelta.
 29. The method of claim 23, further comprising determining themotion vector by adding a motion vector delta to the motion predictorinformation when the pixel accuracy is one that is likely to occur inthe difference video layer.
 30. The method of claim 29, wherein thepixel accuracy is half pixel.
 31. The method of claim 23, furthercomprising determining the motion vector by adjusting a sum of a motionvector delta and the motion predictor information based upon the pixelaccuracy.
 32. The method of claim 31, wherein said adjusting comprisesapplying a weighting factor to the sum of the motion vector delta andthe motion predictor information based upon the pixel accuracy.
 33. Themethod of claim 31, wherein said adjusting comprises increasing the sumwhen the pixel accuracy is likely to occur in the difference videolayer.
 34. The method of claim 33, wherein said adjusting comprisesincreasing the sum when the pixel accuracy is half pixel.
 35. The methodof claim 31, wherein said adjusting comprises decreasing the sum whenthe pixel accuracy is unlikely to occur in the difference video layer.36. The method of claim 35, wherein said adjusting comprises decreasingthe sum when the pixel accuracy is a quarter pixel or smaller.
 37. Themethod of claim 23, further comprising determining context informationfor entropy coding based upon the pixel accuracy.
 38. The method ofclaim 37, further comprising determining a context for entropy coding ofa motion vector delta based on the pixel accuracy.
 39. The method ofclaim 23, wherein the video unit is selected from a group comprising:frame, slice, largest coding unit (LCU), coding unit (CU), block, pixel,and sub-pixel.
 40. The method of claim 23, further comprisingdetermining the value of the video unit by generating a prediction unitfor the video unit.
 41. The method of claim 23, wherein the base layeris a reconstructed base layer.
 42. The method of claim 23, furthercomprising encoding the video unit and signaling the motion predictorinformation in a bitstream.
 43. The method of claim 23, furthercomprising decoding the video unit and receiving the motion predictorinformation in a bitstream.
 44. A computer-readable storage mediumhaving instructions stored thereon that when executed cause an apparatusto: store a difference video layer of pixel information derived from adifference between an enhancement layer and a correspondingreconstructed base layer of the video information; determine pixelaccuracy associated with motion predictor information; determine amotion vector based on the pixel accuracy and the motion predictorinformation; and determine a value of a current video unit based atleast in part on the motion vector.
 45. The computer-readable storagemedium of claim 44, wherein determining the value of the video unitcomprises performing inter prediction for the video unit based on thedifference video layer.
 46. The computer-readable storage medium ofclaim 44, wherein the motion predictor information comprises motionvector predictor information.
 47. The computer-readable storage mediumof claim 46, wherein the motion vector is determined based on the motionvector predictor information, a motion vector delta, and informationassociated with reference video units for the video unit, wherein themotion vector predictor information is associated with the referencevideo units, and the motion vector is determined by adding the motionvector delta and the motion vector predictor information.
 48. Thecomputer-readable storage medium of claim 44, further comprisinginstructions to determine the motion vector by adding a motion vectordelta to the motion predictor information when the pixel accuracy is onethat is likely to occur in the difference video layer.
 49. Thecomputer-readable storage medium of claim 44, further comprisinginstructions to determine the motion vector by adjusting a sum of amotion vector delta and the motion predictor information based upon thepixel accuracy.
 50. The computer-readable storage medium of claim 44,further comprising instructions to determine context information forentropy coding based upon the pixel accuracy.
 51. An apparatus forcoding video information comprising: means for storing a differencevideo layer of pixel information derived from a difference between anenhancement layer and a corresponding reconstructed base layer of thevideo information; means for determining pixel accuracy associated withmotion predictor information; means for determining a motion vectorbased on the pixel accuracy and the motion predictor information; andmeans for determining a value of a current video unit based at least inpart on the motion vector.
 52. The apparatus of claim 51, whereindetermining the value of the video unit comprises performing interprediction for the video unit based on the difference video layer. 53.The apparatus of claim 51, wherein the motion predictor informationcomprises motion vector predictor information.
 54. The apparatus ofclaim 53, wherein the motion vector is determined based on the motionvector predictor information, a motion vector delta, and informationassociated with reference video units for the video unit, wherein themotion vector predictor information is associated with the referencevideo units, and the motion vector is determined by adding the motionvector delta and the motion vector predictor information.
 55. Theapparatus of claim 51, wherein the means for determining the motionvector is further configured to determine the motion vector by adding amotion vector delta to the motion predictor information when the pixelaccuracy is one that is likely to occur in the difference video layer.56. The apparatus of claim 51, wherein the means for determining themotion vector is further configured to determine the motion vector byadjusting a sum of a motion vector delta and the motion predictorinformation based upon the pixel accuracy.
 57. The apparatus of claim51, wherein the means for determining the motion vector is furtherconfigured to determine context information for entropy coding basedupon the pixel accuracy.